The present disclosure concerns systems and methods for detecting the presence of substances in a liquid, such as blood and other bodily liquids. One application of the system and method disclosed herein is to detect the presence of preservation substances, such as DMSO, in a cryogenically-treated blood sample that is being treated to remove the DMSO.
It is known to utilize various cryoprotectants, such as dimethyl sulfoxide (DMSO), during cryopreservation cells. Use of a cryoprotectant is essential to prevent cryoinjury to the cells, such as from the formation of intracellular ice crystals during freezing. Thus, in stem cell transplant treatments, for instance, the stem cells are obtained and frozen, to be later thawed for periodic treatments of a patient affected by cancer or other diseases. In some prior treatments, the frozen-thawed stem cells are injected into the patient, along with the cryoprotectant, because there have been no effective ways to remove the cryoprotectant without losing a significant amount of stems cells or otherwise contaminating them. However, at room or body temperature, certain cryoprotectants, such as DMSO, are known to be toxic to cells as well as the patient. For instance, DMSO is known to cause ill effects in patients, ranging from fever and nausea to violent cramping. In some cases, the presences of cryoprotectant may endanger the patient's life. The potentially dangerous effects of cryoprotectants on the patient has tempered the desirability of using frozen and banked cells or liquids of any type.
One common method for removal of cryoprotectant has been mechanical removal, typically in the form of centrifugation followed by resuspension in a media to remove the cryoprotectant by dilution. However, the mechanical forces introduces during centrifugation result in osmotic stress and cell clumping/lysing, particular for fragile cells. Moreover, the generally open nature of centrifugation may result in bacterial or viral contamination of the cell preparation.
In order to address these problems a closed system has been developed as disclosed in U.S. Pat. No. 6,869,758 (the '758 Patent), assigned to the University of Kentucky Research Foundation. The disclosure of the '758 Patent is incorporated herein by reference. The '758 Patent discloses passing the cryoprotectant-containing liquid through at least one semipermeable hollow fiber membrane contained in a hollow module in a first direction to contact the hollow fiber membrane on at least one interior surface. Concurrently, a liquid which is substantially free of cryoprotectant is passed through the hollow module in a second direction (opposite the first direction) so that the cryoprotectant-free liquid contacts the semipermeable hollow fiber membrane on at least one exterior surface. A diffusion gradient is thus created that transfers the cryoprotectant from the cryoprotectant-containing liquid to the cryoprotectant-free liquid for subsequent removal.
Thus, in the treatment of a frozen-thawed cell suspension containing a cryoprotectant, the hollow module and semipermeable hollow fiber membrane disclosed in the '758 Patent can be connected directly to the source of the suspension. In the case of frozen-thawed blood, the device disclosed in the '758 Patent can be connected to the blood bag in a closed system. The system may incorporate a series of pumps and valves to move the cell suspension liquid and the cryoprotectant-free liquid through the system. Details of one such system are shown in FIG. 2 and described herein.
The system disclosed in the '758 Patent provides a completely closed system for the effective removal of cryoprotectant from a liquid. Since the system relies upon diffusion and the dialysis process, there is no damage to the desired cells if the process is optimally performed. Moreover, the process retains a significant quantity of the original frozen-thawed liquid, again if optimally performed. In order to achieve optimal performance, it is desirable that the cryoprotectant removal process continue only for as long as necessary to reduce the presence of cryoprotectant in the cell suspension to a suitable level. While the closed system is less harmful to the desired cells than the prior mechanical methods, “over-treatment” of the cells can cause damage and reduce the quantity of viable cells. On the other hand, “under treatment” does not remove enough of the cryoprotectant, so that the damaging effects of the cryoprotectant remain. Thus, there is a need for a system and method for determining when the dialysis process is complete.